This invention relates to a device for measuring dynamic balance of a rotor for turbochargers, gas turbines, etc.
FIG. 5 depicts an example of a turbocharger, in which the reference numeral 1 denotes a cantilever rotor composed of a shaft 2 and impellers 3 and 4 fixedly secured to opposite ends of the shaft 2. The rotor 1 is rotatably received by a pair of ball bearings 6a and 6b supported by a housing 7. The ball bearing 6a is engaged with a neck portion 5 of the shaft 2 which is formed adjacent to the impeller 3. The impeller 3 is disposed within a gas feed passage 8 while the impeller 4 is disposed within a gas exhaust passage 9.
In such a turbocharger or the like gas turbine, it is important that the rotor 2 should exhibit good dynamic balance during its rotation, since otherwise the rotation causes vibration of bearings 6a and 6b and other associated parts. Machining errors during manufacture of the impellers, shaft and other components of the rotor generally cause dynamic unbalance of the rotor.
There is known a device which can detect and evaluate the dynamic balance of such rotors. The conventional device includes a housing, two or more ball bearings secured to the housing for rotatably supporting the rotor in a substantially horizontal position, and a sensor for detecting vibration of the housing caused as a result of the rotation of the rotor supported by the bearings.
In the conventional dynamic balance measuring device, the weight of the rotor is supported in the radial direction (in the direction perpendicular to the axis of the rotor shaft) only, because the rotor shaft is maintained in a horizontal position. It has been found, however, that vibration in the thrust direction (in the direction parallel to the axis of the rotor shaft) should not be ignored in order to precisely evaluate the dynamic balance of the rotor. That is, with the conventional device, a portion of the vibration in the radial direction is relaxed as a result of the sliding of the shaft in the axial direction so that the measured value involves a measuring error which cannot be disregarded.